Where two workpiece parts are to be joined together by the above techniques it is usually necessary to overlay one workpiece over the other and to temporarily secure the two workpieces together to allow the joining technique to be performed. This is most simply performed by gripping the two workpiece parts between pairs of jaws. The latter can be urged together so as to grip the workpiece parts using a cam drive and mechanical linkage, typically with an overcentre action so that the clamping action has little tendency to reverse until a positive force is applied to release the overcentre action. However in automated assembly, remotely controllable power operated jaws are required and hitherto it has been commonplace to mount a power unit such as a motor, or piston and cylinder drive means, close to or forming part of the support structure for the jaws and to convey power such as electricity or compressed air or hydraulic fluid to the power unit as appropriate, from a remote source. Appropriate switches or valves control the flow of energy to operate the power unit.
The latter may operate positively so that drive is transmitted to clamp and unclamp the jaws, but single acting drive units may be used with a spring return. Thus for example the power unit may be operated so as to close the jaws against a spring which normally holds them open.
Pneumatic cylinders which are the most popular form of power unit for such devices, but these tend to be bulky and the combination of upright support, power unit, and laterally extending jaws becomes a significant entity which can interfere with access to the workpiece parts by joining tools such as welding guns, riveting guns and the like.
It is therefore a first object of the present invention to reduce the size of a workpiece support as aforesaid so as to increase the access to workpieces clamped between the jaws.
It is another object of the invention to provide a tool plate on which a number of such workpiece holders are mounted together with a tool plate support onto which the tool plate assembly can be mounted and from which the tool plate assembly can be demounted, readily and easily.